The present invention relates generally to electric machines. More specifically, this invention relates to an improved liquid cooling system for an electric machine.
As higher voltage and higher power electric machines are utilized in vehicles and the like, a problem regarding the fact that such electric machines produce an increasing amount of heat is realized. Excess heat must be dissipated to preserve the reliability and efficiency of the electric machine. In many applications, the amount of heat is great enough that a liquid cooling system is used to dissipate heat from the electric machine.
Prior liquid cooling systems have utilized a cooling jacket in thermal contact with the machine, and a fluid is circulated through the cooling jacket to transfer heat from the jacket into the fluid, which then is carried from the cooling jacket to a heat loss device. One type of cooling jacket is a double-walled cast aluminum cooling jacket. The constraints of casting design and fabrication result in a cooling jacket of substantial thickness. Since the overall package size of the electric machine is usually restricted by available space in, for example, a vehicle, the cast cooling jacket thickness is disadvantageous because it limits a space available for the electric machine stator and thereby limits the performance of the electric machine.
A second type of cooling jacket, a brazed steel assembly, has been used in an effort to reduce the cooling jacket thickness. The brazed joints, however, have low mechanical strength and are vulnerable to cracking under vibration, which will result in a fluid leak and potential failure of the electric machine. The brazed cooling jackets are less efficient at heat transfer because the interior of the jackets have a decreased surface area simply due to a smaller diametrical dimension of the outer surface of the cooling jacket as compared to that dimension of the cast jacket, which as noted must be thicker. Additionally, because the interior walls of the brazed cooling jackets are smooth compared to the cast cooling jacket, the result is a less turbulent flow of the cooling fluid through the jacket, and consequently less effective cooling.
Although the normal systems do indeed reduce operating temperatures of electric machines, the art will nevertheless well receive alternative configurations and methods that improve cooling ability, reduce required footprint, reduce cost, or improve longevity.